In the past, it has been possible to measure electric field strengths directly in relatively weak electric fields. Various techniques, such as diodes, have been used to detect microwave electric fields, and to produce a signal indicative of the strength of the electric field. However, presently available diodes do not survive well in strong microwave electric fields, and have been unsuitable for use in such environments. To increase a diode's power handling capability would probably involve increasing the junction area of the semiconductor to the point that the junction capacitance would be too large for effective operation at microwave frequencies.
The need has existed to directly measure strong microwave electric fields, for example in microwave ovens.
Diodes also suffer from a lack of precise spatial readings. Because of the relatively large physical size of a diode, it is virtually impossible to obtain a precise reading of the electric field strength at a particular point. Instead, the output of the diode is generally an average of the electric field strength over the area encompassed by the physical size of the diode. Metal shielded packages for use in a microwave oven may have rapidly diminishing field strengths as one moves away from the metal surface. A probe which is not capable of measuring electric field strengths at a particularly small point will not give accurate measurements under such circumstances.
A need has existed for a probe capable of measuring the electric field strength at a particular small region or point, or on a particular localized surface in a microwave oven.
The electric field is affected by metallic probes and other metallic elements which might be introduced into the oven in order to measure the field. Many available metallic probes change the very field that one is attempting to measure. Thus, the measurement fails to accurately measure the electric field strength, but instead measures the disturbed field strength, which may be significantly different. It is desirable to accurately measure the electric field while disturbing it as little as possible.
The need has also existed for a probe capable of measuring electric field strength in a microwave oven without substantially perturbing the field.
Recent advances in the use of shielded packages and other containers containing metal components in a microwave oven have increased the need for a technique to measure electric field strength in a strong microwave field. Such measurements are necessary for purposes of determining suitable materials for the packaging which is used in a microwave oven, for understanding the function of metal packaging components, for studying problems of arcing, resonance and regenerated fields in a microwave oven, and for other purposes.
Therefore, the need has existed for an apparatus and method capable of measuring strong microwave electric fields without substantially perturbing the field that is being measured.